The driver employing the friction drive method is well known, in which a driving member, formed of a shaft, is non symmetrically reciprocated in its axial direction by the piezoelectric element, whereby a frictionally coupling member, engaging the driving member, and the driving member are caused to slide as a relative movement (there are two cases, one is the frictionally coupling member is moved, the other is the driving member is moved).
Concerning said driver employing the friction drive method, a drive circuit is necessary to be used so that periodically changing voltages are applied to the piezoelectric element. As the drive circuit, an electrode receives the electrical voltages, or is grounded by a semiconductor switching element, whereby the drive circuit applies the electrical voltages, as rectangular waves, to the piezoelectric element.
For example, in Patent Document 1, a drive circuit employing a half-bridge circuit, is disclosed. That is, one electrode of the piezoelectric element is always grounded, and a switching element is configured to connect a power supply to the other electrode. Further, another switching element is configured to connect the ground to the above other electrode. Further, in Patent Document 2, a full-bridge circuit is disclosed, that is, both electrodes of the piezoelectric element are alternately connected to the power supply, and the remaining electrode, not being connected to the power supply during the above alternative connection, is grounded, so that the polarity of the electric voltage, to be applied to the piezoelectric element, is reversed.
The piezoelectric element is a capacitor as the electrical category, more precisely, the piezoelectric element includes a resistor element, which generates adverse heat while charging and discharging operation. Accordingly, when the drivers, employing the above conventional methods, are continuously operated, adverse problems occur. That is, after continuous operation, the temperature of the piezoelectric element increases, so that adhering force is reduced to connect the piezoelectric element with a spindle to fix the driving member or the piezoelectric element, which results in an adverse affect on the mechanical structure. Further, the temperature of the piezoelectric element reaches Curie temperature, so that a extending and contracting function is deteriorated, whereby the function of the piezoelectric element decreases. Yet further, the switching elements overheat due to charging and discharging electrical current.    Patent Document 1: Unexamined Japanese Patent Application Publication No. 2001-268,951    Patent Document 2: Unexamined Japanese Patent Application Publication No. 2001-211,669